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Fruit and vegetables: Forgotten plant diseases

Until now, genetic engineering methods have been used almost exclusively on crops for which there is an international market. Many pathogens that affect regional crops could be controlled by using genetic engineering methods to develop resistant varieties. However, this is not commercially attractive for big companies. Although there are numerous public research projects in this area, there are hardly any market authorisations on the horizon. One reason for this is the high cost of the approval process.

Sclerotinia blight on a groundnut plant, caused by the Sclerotinia minor fungus
Photo: North Carolina State University

The authors of a study published in nature biotechnology in 2010, assessed global research activity conducted from 2003 to 2008 relating to the use of genetic engineering in regional crops. They list 313 scientific publications and 851 field trials. Research into plant diseases comes top, with 83 articles and 137 field trials.

The GM crops that are currently grown commercially are globally traded bulk commodities: maize, soya, cotton, oilseed rape and sugar. They all come from the laboratories of major conglomerates like Monsanto. The only exceptions are virus-resistant papaya and zucchini, which were developed in the 1990s as part of public research projects and are grown on a small scale in the USA. Breeding improved crops that are only grown regionally is not financially attractive for major companies because the market is not big enough.

Yet there are plenty of plant diseases that cause considerable harvest losses in regional crops, including staple food crops in developing countries, like cassava, but also fruit and vegetable varieties that are grown and consumed in industrial and emerging nations. Genetic engineering offers new possibilities for breeding resistant varieties to combat a range of plant diseases. It is primarily public research facilities that are involved in this area. Numerous projects are being conducted but, with a few exceptions, there is no sign of any of the plants receiving regulatory approval.

From groundnuts to cassava: public research projects

For some time now, scientists from a number of US universities have been working on fungus-resistant groundnuts. The Sclerotinia minor fungus, which causes Sclerotinia blight, is widespread in the US. Affected plants shrivel and wither. To combat the fungus, they have transferred a gene from barley to groundnuts. This gene contains the information for the oxalate oxidase enzyme that plays an important role in fighting off pathogens. The GM groundnuts have been tested in field trials since 2004 and an application has now been submitted for their authorisation.

Oranges that are resistant to Liberibacter bacteria are also being developed in the US. These bacteria are passed on by aphids and cause a disease known as citrus greening. The fruits of affected plants become green and inedible. The disease is widespread in Asia and Africa and was brought to the US at the end of the 1990s, where it now represents a serious threat to orange farming. No natural resistance to the pathogen has been found. A team at the University of Texas has genetically engineered oranges so that they produce a peptide that destroys the bacterial cell walls. The GM orange could be ready for commercial cultivation in around 2016.

The Black Sigatoka fungus and Xanthomonas campestris bacteria are estimated to cause harvest losses to banana farmers of around 50 per cent, and they also attack plantains, which are grown by subsistence farmers in developing countries. Affected banana plants wilt and rot. The national agricultural research agencies of Uganda and Nigeria are developing resistant GM bananas with help from Europe, some of which are already being tested in field trials. The fungus-resistant bananas contain a gene for a chitinase, an enzyme that breaks down the cell walls of fungi. The bacteria-resistant bananas contain genes from peppers, which seal off any plant cells attacked by pathogens so that they cannot spread any further.

Scientists at the Swiss Federal Institute of Technology (ETH) in Zurich have been working for years with African and Asian research institutions to make cassava plants resistant to the cassava mosaic virus, which causes estimated harvest losses of between 30 and 40 per cent. To create the resistance, the researchers insert a gene from the virus genome into the plants. When this gene is expressed in the plant cells and transferred into RNA, a mechanism known as RNA interference causes the corresponding RNA in the virus to break down. This means that the virus can no longer survive. The research is being conducted as part of the BioCassava Plus project, which is being financed by the Gates Foundation.

Obstacles on the road to market

In view of the amount of research activity, the number of GM plants already on the market or likely to be authorised in the foreseeable future is very small. The authors of the 2010 study published in nature biotechnology say this is largely because the authorisation procedures that all GM plants around the world have to pass through are expensive and complicated. A study conducted in 2011 on behalf of the CropLife International industry association calculated that the biosafety research and authorisation procedure associated with a single GM plant costs an average of 36 million US dollars. Sarah Davidson of Cornell University, the associate director of the international Durable Rust Resistance in Wheat project, told the New York Times in 2011 that one would think there would be more modified crops on the market that had been developed by big public universities, but that it was “too expensive”. At the same time, many developing countries do not yet have any legal regulations for authorising GMOs, which also hinders market introduction.

Another incalculable factor for public research institutions is the fact that a large number of plant biotechnology procedures are patented and there could be licence fees to pay. In the past, however, holders of patents have sometimes waived licence fees either partially or in full, as was the case with virus-resistant papaya plants, which were authorised in the US in the early 1990s. The earliest patents have now expired in any case. In 2003 and 2004, US universities founded two organisations that help scientists with patents and authorisation procedures: the Public Intellectual Property Resource for Agriculture (PIPRA) and Specialty Crop Regulatory Assistance (SCRA).

In 2010, for the first time since the 1990s, a GM plant developed through public research was authorised in the US: a plum with resistance to the sharka virus that was brought over from Europe. It was developed by the research department of the USDA. In Brazil, a virus-resistant bean was authorised in 2011 that was developed by Brazil’s national agricultural research agency. However, authorisation does not mean that all the problems have been solved. Public research institutions do not generally have any infrastructure for seed production or marketing. And it is difficult to assess to what extent GM fruit and vegetables will be accepted and bought by consumers.